Bacterial response to oxygen

• can a bacteria grow in the presence of oxygen?

  • no—then these are anaerobes

  • yes—then, does it require oxygen for growth?

    • yes—then these are obligate aerobes

    • no—then these are facultative organisms (or facultative anaerobes, although this is a misnomer)

  • so facultative organisms differ from both the strict aerobes and anaerobes

• Then, ask how these organisms get their energy

  • obligate aerobes can only derive energy from respiration. if they could ferment, then they wouldn’t be called obligate aerobes. an example of this is M. tuberculosis

  • Facultative organisms are broken down into two categories

    • can only ferment: these can grow both anaerobically and aerobically but either way obtain their energy from fermentation

    • can only respire: these can only obtain their energy from respiration, and Pseudomonas aeruginosa is one of these organisms. the reason that it is facultative is that under anaerobic conditions, it uses a terminal electronic acceptor that is not oxygen (in particular, nitrate) to accomplish respiration

    • can ferment and respire: they can ferment or use respiration to make ATP. E. coli is a member of this group

Category: Microbiology Notes